The present invention relates to blow-molded containers of biaxially oriented thermoplastic materials, typically polyethylene terephthalate, that are especially adapted to be filled with a hot liquid or semi-liquid product and hermetically sealed, and which are generally referred to as thin-walled hot-fill containers. The invention particularly relates to improvements in container design to achieve a filled container that, when cooled, retains a desired container configuration despite the development of a partial vacuum within the container, and provides enhanced support of any label applied to the container even when subjected to sidewall impact.
Thin-wall hot-fill containers are typically used for packaging of liquids which must be placed in the container while hot to provide for adequate sterilization. During the filling process, the container is subjected to elevated temperatures on the order of about 85xc2x0 C. and may be subjected to some small positive internal pressures on the order of about 0.2 bar. The container is immediately capped so that no appreciable cooling of the container contents occurs prior to the hermitic sealing. As the product subsequently cools, a negative internal pressure is formed in the sealed container. Any flexible wall of the container will elastically deform inward to the extent necessary to at least partially reduce the negative pressure within the container. Thin-wall hot-fill containers of the prior art typically include a plurality of vacuum panels specially designed to elastically deform in a controlled manner, thus preventing any large uncontrolled shape distortion. The vacuum panels are typically arranged around the circumference of a middle portion of the container and are typically covered by a wrap-around label held within the margins of an area commonly identified as the label panel.
Many styles and geometric patterns have been developed for the vacuum panels. The variations are all intended to address various concerns about the container performance and shape retention when dropped, when vertically stacked, when pinched by manually gripping the container, etc. To address these concerns the vacuum panels often include raised central wall portions, post areas between the vacuum panels, and circumferential land areas above and below the vacuum panels, longitudinal and circumferential recessed ribs, hinge portions, etc. As the wall thickness of the containers is reduced from the already thin dimension of typically less than xc2xd mm, the various problems associated with thin-wall hot-fill containers become exacerbated. A particularly difficult problem is presented by side impacts that tend to permanently deform the sidewall of the container. A more general problem is the competing desires of providing sufficient stiffness in specific areas of the label panel, while still permitting other areas to yield in the intended manner for successful hot-fill performance.
What is needed is a thin wall hot-fill container that provides a large range of flexibility while retaining sufficient support of any label applied to the container even when subjected to sidewall impact.
These competing needs are satisfied by a container of the present invention, which has a closable neck, a shoulder portion situated below the neck, a base, and a body portion connecting the shoulder portion to the base. The body portion includes a label mount area bounded by upper and lower margins. A plurality of vacuum panels are situated in the label mount area with a land area separating each adjacent pair of vacuum panels. Each of the vacuum panels includes an upper edge and a lower edge, each edge being spaced from the upper and lower margins of the label mount area. Each vacuum panel includes an upper area adjacent the upper edge and a lower area adjacent the lower edge, the upper and flower areas of each vacuum panel being mutually asymmetric. As an example, either the upper or lower area of each vacuum panel comprises a horizontally cylindrically concave surface while the other area of each vacuum panel comprises a plane inclined at a shallow angle with respect to a horizontal plane. Additionally, the label mount area includes a circumferential recessed rib located in the land area adjacent to the margin of the label mount area nearest to the end of the vacuum panel including the horizontally cylindrically concave surface.
Each of the vacuum panels of a thin-walled hot-fill plastic container of the present invention includes a central portion joining the upper area and the lower area, the central portion preferably including a central land area and side portions coupling the central land area to the adjacent land areas separating adjacent vacuum panels from each other. In a preferred embodiment, the side portions of each vacuum panel include a tapered geometry from the upper area to the lower area. The tapered geometry can comprise, for example, a conical surface section of decreasing radius of curvature from the upper area to the lower area.
The tapered geometry and the differences between the upper and lower areas evokes a vertically asymmetric pattern to the vacuum panels that achieves a large range of pressure response through varying flexibility without significant movement of the components parts of the vacuum panels. The shallow angled portion at one end of the vacuum panels and the circumferential recessed rib located adjacent to the other end of the vacuum panels provide the required stiffness to resist all but the most significant sidewall impacts, thereby ensuring both the necessary performance and appearance of the container within the margins of the label mount area.